Time from beginning of one pulse to beginning of next pulse
Changing Depth changes PRP
Longer to get to object the greater the PRP

PRF Pulse Repetition Frequency

How many pulses in a second
depth increases prp increases
depth decreases prf increases

Duty Factor

How long in time- pulse duration/PRP x 100
% of time crystals vibrate
99.8% of time the transducer is listening
.2 to .5% transducer is transmitting
Pulse duration decreases
duty factor increases

Shallow Imaging

less listening time
shorter prp
higher prf
higher duty factor

Deeper Imaging

More listening time
longer prp
lower prf
lower duty factor

Logarithms Scales

compare signals

Attenuate - When reporting attenuation in dB, authors will often omit the negative sign. Because attenuation means a weakeneing or a decrease the dB's must be negative

weakening of beam through the body recorded in decibels
attenuation is determined by two factors
Path length and frequency of sound.
Distance and attenuation are directly related

More attenuaton

Longer distances
Higher frequencies

Less Attenuation

Shorter distances
lower frequencies

Soft Tissue
-3dB=2x
-6dB=4x
-9dB=8x
-10db=10x

=1/2
=1/4
=1/8
1/10

Sound wave weakening is determined by

Path Length
Frequency

Incidence Beam
Transmission Beam
Reflected Beam

from the transducer
through the medium
reflected back to the sound source

Three processes that contribute to attenuation

1. Reflection-bouces off
2. Scattering-Rayleigh
3. Absorbtion- 80%

Two forms of reflection are

Specular-smooth
diffuse - rough

Diffuse Reflection

most interfaces in the body are not smooth, but have some irregularities. When wave reflects off an irregular surface, it radiates in more that one direction also called backscatter

Specular Reflection

When boudary is smooth, the sound is reflected in only one direction. Specular reflection occurs when a light wave strikes a mirror. Wave is slightly off axis.

Scattering

the random redirection of sound in many directions. Sound scatters when the tissue interface is small. Higher frequency sound beams scatter much more than lower frequency beams. scattering is directly related to frequency

Rayleigh Scattering

A special form of scattering that occurs when the structure;s dimensions are much smaller that the beams wavelength ie red blood cells result in rayleigh scattering
Rayleigh scattering is organized
when frequecy doubles, rayleigh scatterng is 16 x greater
Rayliegh scattering is related to frequency to the forth power

What is the significance of attenuation in diagnostic sonography?

Higher the frequency sound waves produce shorter pulses, which usually create more accurate images. However, higher frequency sound attenuates more and is less capable of traveling to substantial depths.
Goal: use the highest frequency that still provides images to the depth of the structures od clinical interest

Absorbtion

The third and most sizeable component of attenuation is absorbtion. It occurs when ultrasonic energy is converted into another energy form such as heat. Like scattering, absorbtion is directly related to frequency. higher frequency waves attenuate more than lower frequency waves. Sound traveling in bone undergoes extensive absorption

Atteunuation Coefficient is the number of decibels of attenuation that occurs when sound travels one centimeter

the units of attenuation coefficient are dB/cm decibels per centimeter.

Attenuation coefficient in soft tissue

atten. codf.(dB/cm)=frequency (MHz)/ 2
The attenuation coefficient is one half of the frequency